Chapter 2 PowerPoint Slides

ISBN 0-13-146913-4Prentice-Hall, 2006

Chapter 2

Modeling the Process and LifeCycle

Copyright 2006 Pearson/Prentice Hall. All rights reserved.

Pfleeger and Atlee, Software Engineering: Theory and Practice

Page 2.2© 2006 Pearson/Prentice Hall

Contents

2.1 The Meaning of Process2.2 Software Process Models2.3 Tools and Techniques for Process

Modeling2.4 Practical Process Modeling2.5 Information System Example2.6 Real Time Example2.7 What this Chapter Means for You



Chapter 2 Objectives

• What we mean by a “process”• Software development products, processes,

and resources• Several models of the software

development process• Tools and techniques for process modeling



2.1 The Meaning of Process

• A process: a series of steps involving activities, constrains, and resources that produce an intended ouput of some kind

• A process involves a set of tools and techniques



2.1 The Meaning of ProcessProcess Characteristics

• Prescribes all major process activities• Uses resources, subject to set of constraints (such

as schedule)• Produces intermediate and final products• May be composed of subprocesses with hierarchy

or links• Each process activity has entry and exit criteria• Activities are organized in sequence, so timing is

clear• Each process has guiding principles, including

goals of each activity• Constraints may apply to an activity, resource or

product



2.1 The Meaning of ProcessThe Importance of Processes

• Impose consistency and structure on a set of activities

• Guide us to understand, control, examine, and improve the activities

• Enable us to capture our experiences and pass them along



2.2 Software Process ModelsReasons for Modeling a Process

• To form a common understanding• To find inconsistencies, redundancies,

omissions• To find and evaluate appropriate activities

for reaching process goals• To tailor a general process for a particular

situation in which it will be used



2.2 Software Process ModelsSoftware Life Cycle

• When a process involves building a software, the process may be referred to as software life cycle– Requirements analysis and definition– System (architecture) design– Program (detailed/procedural) design– Writing programs (coding/implementation)– Testing: unit, integration, system– System delivery (deployment)

– Maintenance



2.2 Software Process ModelsSoftware Development Process Models

• Waterfall model• V model• Prototyping model• Operational specification• Transformational model• Phased development: increments and

iterations• Spiral model• Agile methods



2.2 Software Process ModelsWaterfall Model

• One of the first process development models proposed

• Works for well understood problems with minimal or no changes in the requirements

• Simple and easy to explain to customers• It presents

– a very high-level view of the development process– sequence of process activities

• Each major phase is marked by milestones and deliverables (artifacts)



2.2 Software Process ModelsWaterfall Model (continued)



2.2 Software Process ModelsWaterfall Model (continued)

• There is no iteration in waterfall model• Most software developments apply a great

many iterations



2.2 Software Process ModelsSidebar 2.1 Drawbacks of The Waterfall Model• Provides no guidance how to handle changes

to products and activities during development (assumes requirements can be frozen)

• Views software development as manufacturing process rather than as creative process

• There is no iterative activities that lead to creating a final product

• Long wait before a final product



2.2 Software Process ModelsWaterfall Model with Prototype

• A prototype is a partially developed product• Prototyping helps

– developers assess alternative design strategies (design prototype)

– users understand what the system will be like (user interface prototype)

• Protopyping is useful for verification and validation



2.2 Software Process ModelsWaterfall Model with Prototype (continued)• Waterfall model with prototyping



2.2 Software Process ModelsV Model

• A variation of the waterfall model• Uses unit testing to verify procedural design• Uses integration testing to verify architectural

(system) design• Uses acceptance testing to validate the

requirements• If problems are found during verification and

validation, the left side of the V can be re-executed before testing on the right side is re-enacted



2.2 Software Process ModelsV Model (continued)



2.2 Software Process ModelsPrototyping Model

• Allows repeated investigation of the requirements or design

• Reduces risk and uncertainty in the development



2.2 Software Process ModelsOperational Specificiation Model

• Requirements are executed (examined) and their implication evaluated early in the development process

• Functionality and the design are allowed to be merged



2.2 Software Process ModelsTransformational Model

• Fewer major development steps• Applies a series of transformations to change

a specification into a deliverable system– Change data representation– Select algorithms– Optimize– Compile

• Relies on formalism• Requires formal specification (to allow

transformations)



2.2 Software Process ModelsTransformational Model (continued)



2.2 Software Process ModelsPhased Development: Increments and Iterations

• Shorter cycle time• System delivered in pieces

– enables customers to have some functionality while the rest is being developed

• Allows two systems functioning in parallel– the production system (release n): currently

being used– the development system (release n+1): the next

version



2.2 Software Process ModelsPhased Development: Increments and Iterations(continued)



2.2 Software Process ModelsPhased Development: Increments and Iterations(continued)• Incremental development: starts with small

functional subsystem and adds functionality with each new release

• Iterative development: starts with full system, then changes functionality of each subsystem with each new release



2.2 Software Process ModelsPhased Development: Increments and Iterations(continued)• Phased development is desirable for several

reasons– Training can begin early, even though some

functions are missing– Markets can be created early for functionality that

has never before been offered– Frequent releases allow developers to fix

unanticipated problems globaly and quickly– The development team can focus on different

areas of expertise with different releases



2.2 Software Process ModelsSpiral Model

• Suggested by Boehm (1988)• Combines development activities with risk

management to minimize and control risks• The model is presented as a spiral in which

each iteration is represented by a circuit around four major activities– Plan– Determine goals, alternatives, and constraints– Evaluate alternatives and risks– Develop and test



2.2 Software Process ModelsSpiral Model (continued)



2.2 Software Process ModelsAgile Methods• Emphasis on flexibility in producing software

quickly and capably• Agile manifesto

– Value individuals and interactions over process and tools

– Prefer to invest time in producing working software rather than in producing comprehensive documentation

– Focus on customer collaboration rather than contract negotiation

– Concentrate on responding to change rather than on creating a plan and then following it



2.2 Software Process ModelsAgile Methods: Examples of Agile Process

• Extreme programming (XP)• Crystal: a collection of approaches based

on the notion that every project needs a unique set of policies and conventions

• Scrum: 30-day iterations; multiple self-organizing teams; daily “scrum” coordination

• Adaptive software development (ASD)



2.2 Software Process ModelsAgile Methods: Extreme Programming

• Emphasis on four characteristics of agility– Communication: continual interchange between

customers and developers– Simplicity: select the simplest design or

implementation– Courage: commitment to delivering functionality

early and often– Feedback: loops built into the various activitites

during the development process



2.2 Software Process ModelsAgile Methods: Twelve Facets of XP

• The planning game (customer defines value)

• Small releases• Metaphor (common

vision, common names)

• Simple design• Writing tests first• Refactoring

• Pair programming• Collective ownership• Continuous

integration (small increments)

• Sustainable pace (40 hours/week)

• On-site customer• Coding standards



2.2 Software Process ModelsSidebar 2.2 When is Extreme Too Extreme?

• Extreme programming's practices are interdependent – A vulnerability if one of them is modified

• Requirements expressed as a set of test cases must be passed by the software– System passes the tests but is not what the

customer is paying for• Refactoring issue

– Difficult to rework a system without degrading its architecture



2.2 Software Process ModelsSidebar 2.3 Collections of Process Models• Development process is a problem-solving

activity• Curtis, Krasner, and Iscoe (1988) performed a

field study to determine which problem-solving factors to captured in process model

• The results suggest a layered behavioral model as supplement to the traditional model

• Process model should not only describe series of tasks, but also should detail factors that contribute to a project's inherent uncertainty and risk



• Notation depends on what we want to capture in the model

• The two major notation categories– Static model: depicts the process– Dynamic model: enacts the process

2.3 Tools and Techniques for Process Modeling



• Elements of a process are viewed in terms of seven types– Activity– Sequence– Process model– Resource– Control – Policy– Organization

• Several templates, such as an Artifact Definition Template

2.3 Tools and Techniques for Process ModelingStatic Modeling: Lai Notation



• Enables enaction of process to see what happens to resources and artifacts as activities occur

• Simulate alternatives and make changes to improve the process

• Example: systems dynamics model

2.3 Tools and Techniques for Process ModelingDynamic Modeling



2.4 Practical Process ModelingDesirable Properties of Process Modeling Tools and Techniques

• Facilitates human understanding and communication

• Supports process improvement• Supports process management• Provides automated guidance in performing

the process• Supports automated process execution



2.7 What this Chapter Means for You• Process development involves activities,

resources, and product• Process model includes organizational,

functional, behavioral, and other perspectives

• A process model is useful for guiding team behavior, coordination, and collaboration

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